In the automatic testing of integrated circuits (IC) and other electronic devices, special device handlers have been used which brings the device to the proper temperature and places the device to be tested in position. The electronic testing itself is provided by a large and expensive automatic testing system which includes a test head which has been required to connect to and dock with the device handler. In such testing systems, the test head has been usually very heavy--on the order of 40 to 300 kilograms. The reason for this heaviness is that the test head uses precision high frequency control and data signals so that the electronic circuits must be located as close as possible to the device under test. Accordingly, the test head has been densely packaged with electronic circuits in order to achieve the accurate high speed testing of the sophisticated devices.
Test head positioner systems may be used to position the test head with respect to the device handler. When the test head is accurately in position with respect to the device handler, the test head and the device handler are said to be aligned. When the test head and device handler are aligned, the fragile test head and device handler electrical connectors can be brought together (i.e. docked), enabling the transfer of test signals between the test head and the device handler. Prior to docking, the fragile test head and device handler electrical connectors must be precisely aligned to avoid damaging the fragile electrical connectors.
Test head positioners are designed in several configurations, each configuration being desirable for a particular purpose. In a tumble mode positioner, the test head pivots (or tumbles) about two oppositely disposed pivot points within a cradle. This enable the user to tumble the test head in the cradle from a position where the device handler interface board is up (for interface to horizontal plane handlers from the bottom), through 180 degrees, to a position where the device handler interface board is down (for interface to horizontal plane handlers from the top). In a cable pivot mode positioner, the test head pivots on the axis of the test head cables. Compared to the tumble mode positioner, a cable pivot mode positioner allows the use of reduced cable lengths.
An example of a tumble mode positioner is disclosed in a previous patent by Smith (U.S. Pat. No. 4,705,447), herein incorporated by reference. This patent discloses a positioner assembly which enables a test head to be moved for docking and undocking with respect to three vertical axes. In an alternative embodiment, the test head may be moved for docking and undocking with respect to two vertical axes and one horizontal axis. Thus, in either embodiment, the test head may be manipulated with six degrees of freedom with respect to the center of the plane defined by the test head electrical interface.
Problems have been incurred in easily moving the heavy test head accurately into position with respect to the device handler mechanism. A common lock may prohibit both vertical motion and rotational motion of the test head about a main shaft. To move the test head vertically, the common lock is loosened, thus permitting rotational movement of the test head. Similarly, to rotate the test head, the common lock is loosened, thus allowing the test head to move vertically. However, when a test head is temporarily moved away from the device handler (i.e. undocked) so that adjustments or repairs can be made, both the vertical and the rotational position of the test head may need readjustment to ensure that the test head is aligned with the device handler. The large variety of orientations which the test head may assume may overwhelm an unskilled operator, thus making realignment difficult.
Additional problems have been incurred in realigning the test head and the device handler after the test head has been moved away for repairs or adjustments. Some prior art manipulators include an additional point of rotation (i.e. an additional link) between the main shaft and the test head. By creating an additional link, the test head can be rotated about the axis defined by the link, thus maintaining the relative orientations of the remaining parts of the positioner. However, by adding additional links, the distance between the main shaft and the test head is increased, thus increasing the torque which is imposed by the test head on the main shaft bearings. Thus, the main shaft bearings, main shaft and main arm must become larger and more expensive to provide eased movement and reduced friction between manipulator parts under a greater load.
Examples of cable pivot mode positioner are disclosed in a previous patent by Holt (U.S. Pat. No. 4,893,074), herein incorporated by reference. FIG. 1 and FIG. 2 of this patent shows a first type of cable pivot mode positioner which is referred to as an opposite end cable pivot (OECP) style cradle assembly. As shown in FIG. 1 and FIG. 2, the test head is held at its center of gravity by the positioner. The cable and positioner are attached to the test head on opposite ends of the test head. Because the centerline of the device under test is desirably physically close to the centerline of the electrical outputs of the test head (located near the physical center of the test head) the OECP style cradle assembly may be inappropriate for use with large device handlers. This is because the OECP style cradle assembly cannot access, from underneath, horizontal plane handlers which are built like two pedestal office desks; the positioner stands where one pedestal of such a desk would be located. If the test head were to be projected away from the positioner assembly's support column so that the centerline of the device under test was physically close to the physical center of the test head, pivoting would not occur at the center of gravity of the horizontal wrist shaft, resulting in an unbalanced system.
FIG. 3 of the '074 patent shows a second type of cable pivot mode positioner which is referred to as a cable pivot with center of gravity offset (CPCG) style cradle. The CPCG style cradle allows somewhat more projection of the test head than the OECP style cradle. However, as with the OECP style cradle, the CPCG style cradle is unable to sufficiently project the test head without imposing overwhelming torque on the positioner assembly.
Thus, to solve the interface problem, it is desirable to project the electrical output of the test head a large distance under or over the physically large handlers or probers so that the positioner itself can stand clear of the handlers or probers to which the test head is interfaced. It is also important to continue to enable the test head to pivot with six degrees of motion freedom about the center of gravity of the test head and cable assembly.
For purposes of considering patentability, a brief patentability search was conducted. The patents identified to be of possible interest in the search were:
______________________________________ Patent No. Inventor ______________________________________ 3,262,593 William Hainer 4,345,847 Schiff et al. 4,229,136 Hugo Panissidi 4,132,318 Wang et al. 3,128,887 Guennec et al. ______________________________________